A.Don Fugler, a senior
researcher with the Canada Mortgage and Housing
Corp. in Ottawa, Ontario, responds: If you
leave a house deserted in winter, the biggest risks
are to finishes and furniture due to cold
temperatures and extreme humidity (high or low).
The safest, most convenient way to minimize
problems is to provide a modicum of heating. Keep
it to about 50°F
(10°C). If you build an
energy-efficient house with good solar gains, the
heating costs for the unoccupied winter periods
will be low, and you will avoid the inconvenience
of draining plumbing and removing all water-based
stored foods and supplies. A small amount of
continuous ventilation is also useful for keeping
the air fresh. (I agree that a hydronic heating
system might be risky in this situation.)
If your customers are intent on leaving the
house unheated, there are some precautions I would
recommend. Ventilation is particularly important.
Running an efficient set of fans (a ducted HRV, for
example ) continuously at low speed will mix air
and keep the house fresh. Also, you do not want
solar gain in an unheated house, because
temperature swings can cause condensation problems.
If possible, minimize solar gain by using exterior
shutters on at least the south and west windows.
Before the owners reoccupy the house in winter,
they should have someone bring it up to temperature
slowly over a couple of days. I would not use the
no-heat strategy during the first winter after
construction, because there may still be
significant moisture in the concrete, drywall, and
lumber. A cold or freezing house with high internal
moisture is a recipe for trouble.